Glutathione (GSH) is an important and abundant reducing agent in plants. GSH is involved in tolerance and adaptation toenvironmental stresses, including drought, pollution and temperature extremes.The rate-limiting step in GSH production is catalysed by ga mma-glutamylcysteine synthetase (GCS). In Arabidopsis, twoGSH-deficient mutants define a single locus, ROOT MERISTEMLESSI (RML1)/CADMIUM SENSITIVE2 (CAD2),encoding GCS. The rmll mutant contains 2% of wild-type GSH levels and although embryonic development is normal,on germination, rmll root cells fail to divide and consequently do not maintain the root meristem. In contrast, shootdevelopment proceeds relatively normally. The rmll phenotype is rescued by exogenous GSH (but not other reductants)indicating the specific importance of GSH in root cell division. Moreover, wild-type plants phenocopy rmll whendepleted of GSH by a specific inhibitor of GCS, buthionine sulfoximine (BSO). In tobacco cell culture, BSO treatmentcauses a specific arrest in cell division a t a Gl checkpoint during the cell cycle. These results show a clear link betweencell cycle progression and GSH levels in cell cultures and in the root meristem. Here we propose to analyse its nature andmechanism by (a) establishing which known cell cycle g enes respond to GSH levels, (b) identifying novel genes that areaffected by GSH levels by using microarrays and (c) analysing the novel genes to find which are upstream regulators ofcell cycle targets. To achieve these aims we will use the specific GCS inh ibitor, buthionine sulfoximine, to deplete GSHlevels in the novel synchronizable MM1 and MM2d Arabidopsis cell lines in combination with the rmll and cad2mutants and examine gene expression. During this project the candidate will gain valuable scientific t raining (ingenomics, bioinformatics and cell biology) and professional training (through presentations and the host institution'spersonal development #'
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